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.. 1. 2. 2 Randomized Seeding Design ~ A complete change in operational routine was made for the--1~_~8-69 S~~~SO!!, with ran_domi~ed seeding for only one hour of a six-hour intensive data colle~- tion block. Seeding modes included ground gen~_rators at_.Mt. Harr~s, and aircraft seeding, using droppable pyrotechnics or wing flares. Under~ this seeding desIgri-;--the seeding releases were sufficiently short in duration re- lative to the unseeded periods to allow the collection of both seeded and truly unseeded data. Thus, significant results were obtained using this design. 1. 3 Development and Use of Special Equipment and Observing Techniques It was recognized at the outset that if the project objective were to be accom- plished in the short span of allotted time, high resolution measurements of precipitation rates and vertical profiles of wind, temperature, humidity and stability would be required. Also helpful in isolating seeding effects would be supporting physical measurements such as ice nucleus counts, silver-in- precipitation, and the presence .(or absence) of silver iodide particles acting as snow crystal nuclei. Therefore, a number of special techniques were developed or adapted for use in the experiments. 1. 3. 1 Precipitation Rate Measurements " An optical snow-rate sensor with 2 minute time resolution, capable of opera- ting remotely for a week, was developed and used extensively throughout the project in a dense data collection network. Modified weighing bucket gauges, special Soil Conservation Service snow course water equivalent measurements, and snow pillows were also used as backup data (but with less time resolution). . 1. 3. 2 Ice Nucleus Measurements and Inert Tracers Surface measurements of free air ice nucleus count were made continuously during operational periods at Rabbit Ears Pass, and frequently at additional locations, using an NCAR-Bollay acoustical ice nucleus counter. Phosphor- escent zinc cadmium sulfide was frequently released as a dual tracer simul- taneously with AgI releases during the 1965-66 season, and collected snow samples were melted and analyzed for phosphorescence with the aid of a sen- sitive photo-multiplier device. On a few occasions during the past three seasons, lithium stearate was released as an inert tracer. Air samples were sensed at Rabbit Ears Pass for lithium with a flame photometer, in a cooperative program with the State University of New York at Albany. 1. 3. 3 Snow Sample Collection and Analysis .. During the course of the project two thousand snow samples were collected on 3 ft. x 3 ft. plastic sheets at 5 to 30 minute intervals. These were subse- . 3 .........~n. ~